Reflector mercury lamp



United States Patent O REFLECTOR WRCURY LAMP Elton A. Linsday and DonaldR. Phillips, Cleveland Heights, Ohio, assignors to General ElectricCompany, a corporation of New York 'Ihis invention relates tohigh-pressure mercury vapor lamps of the reflector type wherein an arctube is mounted in a glass bulb provided with a reilecting coating forconcentrating the light in a desired direction and pattern.

In high-pressure mercury vapor lamps used for general illumination, thebulb or outer jacket which encloses the arc tube keeps air away from thearc tube seals and provides mechanical protection while serving also asa heat conservator and short-wave ultraviolet filter. In the reliectortype lamps, the glass bulb is formed to a bowl shape extended at one endinto a reduced diameter tubular neck portion to which is generallyattached a screw type base for accommodating the lamp in a standardsocket. The bowl portion is silvered to reiiect the light along thelongitudinal axis in a controlled beam. The practice up to the presenttime in reflector type lamps has been to mount the arc tube along thelongitudinal axis of the bulb in the same fashion as with non-reflectortype bulbs. For convenience of description, this mode of mounting willbe referred to as vertical mounting inasmuch as in normal usage for highbay lighting, the longitudinal axis is aimed down.

In high bay lighting it is desirable to concentrate the light downwardand to reduce as much as possible the light radiated at angles justbelow the horizontal. Typically, it may be desirable to concentrate thelight in the to 60 zone, that is from the vertical up to 60 therefrom,and to reduce to a low value light radiated in the 60 to 90 zone. In thereflector type mercury vapor lamps which have been available up to thepresent time, for instance in that designated commercially H400Rl, therehas been substantial radiation in the 60 to 90 zone, for instance up to25% of the total lumens from the lamp.

The object of the invention is to provide a new and improved reflectortype mercury vapor lamp which makes more elective utilization of thelight generated by the arc tube.

A more specific object of the invention is to provide a reilector typemercury vapor lamp which provides a more effective concentration oflight in the 0 to 60 zone and reduces glare by decreasing the lighttransmitted in the 60 to 90 zone.

As a result of extensive photometric tests, We have discovered that asubstantial improvement in the utilization of light from reflector typemercury vapor lamps may be eected by mounting the arc tube horizontally,that is transversely to the longitudinal axis of the reflector bulb,rather than vertically as has been the practice up to the present. Thereflector bulb commonly used for the present lamp is formed as a surfaceof revolution along the longitudinal axis. It has a narrow tubular neckportion extending along the axis which opens into a wide flaring bowlportion closed by a light-transmitting convex end face. The neck portionnext to the bowl and the bowl portion out to its region of maximumdiameter is coated with a light-reflecting layer. The arc tube has anoverall length greater than the diameter of the neck- "ice portion andless of course than the diameter of the bowl portion where it is locatedbut amounting to at least a substantial proportion of the axial lengthof the bowl portion. The axial length of the bowl portion is equal to orless than its maximum diameter. With a reliector bulb and an arc tube ofthese relative dimensions, it is possible to reduce the lighttransmission in the glare producing 60 to 90 zone while maintaining thearc tube vertical by moving it further up towards or into the neck ofthe bulb. However, this result is achieved at the cost of a reduction inthe total light output from the lamp. By mounting the arc tubehorizontally in accordance with our invention, a reduction of light inthe 60 to 90 zone is achieved, but advantageously combined with anincrease of light in the 0 to 60 zone, and therefore with an actualimprovement in the utilizable light output from the lamp.

For further objects and advantages and for a detailed description of apreferred embodiment of the invention, attention is now directed to thefollowing description and accompanying drawing. The features of theinvention believed to be novel will be more particularly pointed out inthe appended claims.

In the drawing:

Fig. l is a front elevation View of a reflector type highpressuremercury vapor lamp embodying the invention.

Fig. 2 is a plan view of the arc tube of the same lamp showing part ofthe supporting mount structure therefor.

' Fig. 3 is a graph comparing the candlepower distribution curve of thelamp of Fig. l with that of a prior rellector type lamp.

Referring to Fig. l of the drawing, the lamp illustrated thereincomprises a glass bulb 1 having a tubular reduced diameter neck portion2 to the end of which is sealed a re-entrant stem 3 having a press 4through which'extend relatively stift inlead wires 5, 6. To the upperend of the neck is cemented the usual screw type base 7, the

inleads 5, 6 being connected respectively to the threaded` shell 8 andinsulated center contact 9 thereof.

The neck portion 2 extends downwardly into a tlaring bowl portion 11which terminates at the plane MM where it achieves its maximum diameter.The glass bulb 1 is symmetrical and formed as a surface of revolutionabout the longitudinal axis LL. The bowl portion 11 is formedprincipally of a minor radius A portion at the shoulder and a majorradius B portion forming the sides down to the plane of maximum diameterMM. The shoulder is merged into the neck through a reverse curve formedwith a relatively short radius C. The bowl portion is coated with alight-transmitting layer 12, for instance an internal coating of silver,from the region 13 in the neck portion approximately to the maximumdiameter plane MM. The light-transmitting convex end face 14 is formedto a relatively long radius D which is merged into the radius B of thebowl portion through shorter radii E.

The inner arc tube 1S within the bulb 1 is made of quartz and contains asmall quantity of mercury and a rstarting Igas such as argon. The arcdischarge takes place through main thermionic electrodes 16, 17 atopposite ends of the arc tube, an auxiliary electrode 18 being providedat one end to facilitate starting. 'I'he arc tube illustrated has itsends closed by pinch seals 21, 22 through which extend molybdenum foilswhich have internal extensions into the arc tube to support theelectrodes and external extensions to provide current terminals. v

The arc tube has an overall length greater than the diameter of the neckportion of the retiector bulb, and comparable to the axial length of thebowl portion. The axial length may be taken as the distance measured fthereof.

'the 60 to 90 zone.

along the axis from the juncture of the bowl portion with the neckportion, to the maximum diameter plane MM. The juncture of the bowl andneck portions may also be taken as occurring Where a smooth curvetangent to the Vshoulder curves of radius A would out o the .neckportion. In general the invention is most advantageous with bulbs havinga reflecting bowl portion with an -axial length in the range of 50% to100% of its maximum diameter, and With an overall arc tube `length not:substantially less than the axial length of the bowl portion, forinstance not over 30% less. VIn the illustrated embodiment, .the axiallength of the bowl portion is approximately 27a the maximum diameter,and the overall length of the arc tube is roughly equal to the axiallength of the bowl portion, being in fact about greater.

YThe arc tube must be inserted axially through the neck portion anduthereafter tilted into a horizontal position. This may be achievedthrough the mount structure shown which comprises wire collars 23, 24Wrapped around seals 21., 22 at the regions where they are neckedslightly next Vthe-ends -o'f .thearc tube proper. The ends of wirecollar 23 are formed into an eyelet 25 which provides a hinge connectionto the laterally olset end of mount support rod'26 Welded to inlead 5 ofthe bulb. The ends of wire lcollar v24 are formed into a loop 27 whichmake a sliding lit on mount support rod 28 likewise welded to inlead 5.

To insert the arc tube and mount structure into the bfulb, the .arc tubeis pivoted at 25 on mount support rod 26 .and loop 27 is slid up mountsupport rod 28. :Rods 26 and .2S are manually squeezed together with thearc tube pivoted into an acute angle to the axis of the stem. In thisposition, the arc tube and mount assembly .can be inserted through theneck of the bulb. Once inside the bulb, the arc tube is pivoted into ahorizontal position by reaching in through the neck with a slender rodand forcing the uptilted end of the are tube down so that .loop 27slides down along mount support rod 28 -until it latches ,into the openhook 29 formed in the end The rods 26, 28 are thus forced apart andtheir tendency lto spring back together exerts pressure on -eyele't .25.and loop 27 which holds the arc tube in 'horizontal alignmentintermediate the maximum diameter of .the-'bowl portion and its juncturewith the neck portion.

A .heat disk 31 of polished metal previously welded by tab 32 Vtosupport rod 26 and provided with a slotted aperture `33 accommodatingsupport Wire 28, is then bent down normal to the axis of the lamp so asto close `the lneck of the bulb and reflect both radiant heat andylightback into the bowl .portion ll of the bulb.

rPhe electrical connections to the arc tube are made through inlead 5and mount support rod 26 to wire collar .23 and thence through exiblestrap 34 to main lelectrode 16; and through mount support rod 28 to Wirecollar 24 and thence through current limiting resistor 35 to .auxiliarystarting electrode 13. The connection from inlead 6 to the other mainelectrode 17 is made through aflexible wire 36 which is sheathed withglass tubing `insulators 37 in the region where the wire goes throughslot 33 in heat disk 3l, the insulators being retained in `place on thewire by a crimped tab 33.

-For best results, the arc tube should be supported in a plane .about`midway between the maximum diameter region of the bowl portion at MMWhere the reecting coating terminates and the upper end of the Abowlportion or Vits juncture with the neck portion about Where heat diskl islocated. If the arc tube is lowered 'too much into the howl portion,there is more spreading ,of light beyondthe 0 to 60 zone and more Vglarein On the other hand, if the arc tube is raised too high into the (bowlportion towards .the neck, trapping Aof light occurs resulting in areduction in 'the total utilizable light output from the lamp. jBymountingthe Varc tube horizontally as illustrated,

the improved eiciency of the reflector system more than compensates forthe fact that there are some losses in the total lumens produced (by thearc tube when changing from a vertical to a horizontal mounting. It isknown that when an arc tube is operated horizontally, there is a loss ofabout 4.5% in eciency, for example from 44.7 to 43.0 lumens per vWatt(these figures have reference to the total light output from the arctube mounted in a clear container and without reference to a rellectortype envelope). It is also known that horizont-al operation causes a.decrease of about 2.6% in lamp Wattage when operated from a typicalballast due to increase of the voltage drop across the arc tube at agiven current. These results .are due to the tendency of the arc orluminous chord within the arc tube to bend upward closer to the sidewall of the tube, resulting in lengthening of the arc and operation at acooler temperature Where the efficiency of generation of light is less.Thus previous studies lead to the expectation of a total reduction in.light output of approximately 7% in changing over from vertical tohorizontal operation of the 'are tube. Desp-ite these .unfavorableindications, we have found in the rellector type lamps of the presentinvention Aan increase in utilizable light output, that is in the light.radiated in the 0 to 60 zone, of approximately 24%. Further, We havefound a reduction of light in the 360 to zone of `approximately 75%,thereby reducing the glare .by a factor of almost 4 to 1.

Table l below gives the percent lumens obtained in the various zoneswith comparable reflector type lamps, in the one case rwith a verticallymounted arc tube according to prior practice, and in the other With ahorizontallymounted arc tube according to the present invention.

Table I Percent Total Lumens Zone (Degrees) Vertical Horizontal Thereflector bulb in `each case has the configuration illustrated in Fig. lwith an overall length of approximately 111/2, a maximum diameter of thebowl portion of 6.5", and an axial length of the bowl portion ofapproximately 4.4". The arc tube in each case has an overall length of4.8" measured to the ends of the seals, an outer diameter of 0.8" and anarc gap length between the tips'of the electrodes of .approximately2.5". In the case of the vertically mounted arc tube, the lamp has alight center length, that is a distance measured from the center contact9 of the base to the center of the arc tube `of V7%2 for thehorizontally mounted arc tube, the light center length is 7%".

Fig. 3 illustrates the comparative candlepower d1stribution obtainedwith the lamps. Curve 40 gives the candlepower distribution of thereflector type lamp with the vertically mounted arc tube, whereas curve41 gives that of the lamp having the horizontally mounted arc tube inaccordance with the present invention. It Will v'be observed that -curve40 shows substantial candle- 0f @92.0116 at the unit sphere surface,increases from 0 t0 90, and equalizes the total lumens represented bythe two curves.

Curves 40 and 41 were determined with the lamp rotating within aphotometer in order to obtain the mean candlepower around the axis ofthe lamp at the various angles of elevation. With the horizontallymounted arc tube, the beam patter is not perfectly circular but shows aslightly elliptical distribution of intensity in a horizo-ntal planewith the major axis oriented in the plane of the axis of the arc tube.By providing a light frosting to the convex end face 14 of the bulb, thedistribution of intensity in a horizontal plane can -be made more nearlyuniform and patterns and shadows in the light cone substantiallyeliminated. For this purpose we prefer to use a frost known in the tradeas a No. 4 frost just suicient to blur the outlines of the arc tube whenseen through the end face of the bulb.

While a certain specific embodiment of the invention has been shown anddescribed in detail, it is intended primarily as illustrative and not aslimitative of the invention. Various modifications for adapting thepresent construction tutilizing a horizontally mounted arc tube within areflector type bulb to other sizes and ratings of arc tubes withappropriate reflector bulbs will readily suggest themselves to thoseskilled in the art. It will be understood furthermore that the inventionis not to be regarded as limited to the specific tilting frame and mountsupport combination which has been described for allowing the arc tubeto be inserted through the narrow neck of the bulb. The appended claimsare intended to cover any modifications coming within the true spiritand scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electric lamp comprising a glass bulb generally symmetrical aboutits longitudinal axis and having a tubular neck portion extending alongsaid axis and opening into a flaring bowl portion closed by alight-transmitting convex end face, said bowl portion being coated witha light-reflecting layer approximately up to its region of maximumdiameter and having an axial length from 50% to 100% of its maximumdiameter, an elongated mercury vapor arc tube within said bulb having anoverall length greater than the diameter of said neck portion and notover 30% less than the axial length of said bowl portion, and a mountsupporting said arc tube within the bowl portion transversely to saidlongitudinal axis and in a plane about midway between the maximumdiameter of the bowl portion and its juncture with the neck portion.

2. A reflector type mercury vapor lamp comprising a glass bulb forming asurface of revolution about its longitudinal axis and having a narrowtubular neck portion extending along said axis terminated at one end bya base and opening at the other into a flaring bowl portion, alight-transmitting convex end face closing the maximum diameter end ofsaid bowl portion, said bowl portion being coated with alight-reflecting layer approximately up to its region of maximumdiameter and having an axial length from to 100% of its maximumdiameter, a high pressure mercury vapor arc tube within said bulbcomprising an elongated vitreous tube having an overall length greaterthan the diameter of said neck portion and approximately equal to theaxial length of said bowl portion, and a mount supporting said arc tubewithin the bowl portion transversely to said longitudinal axis and in aplane about midway between the maximum diameter region of the bowlportion and its juncture with the neck portion.

3. A reflector type mercury vapor lamp comprising a glass bulb forming asurface of revolution about its longitudinal axis and having a narrowtubular neck portion extending along said axis terminated at one end bya base and opening at the other into a flaring bowl portion, alight-transmitting convex end face closing the maximum diameter end ofsaid bowl portion, said bowl portion being coated with alight-refiecting layer approximately up to its region of maximumdiameter and having an axial length about its maximum diameter, ahigh-pressure mercury vapor arc tube within said bulb comprising anelongated vitreous tube having an overall length greater than thediameter of said neck portion and approximately equal to the axiallength of said bowl portion, and a mount supporting said arc tube withinthe bowl portion transversely to said longitudinal axis and in a planeabout midway between the maximum diameter region of the bowl portion andits juncture with the neck portion.

4. A lamp as defined in claim 3 having a light frosting on the convexend face.

References Cited in the file of this patent UNITED STATES PATENTS1,031,114 Gilmore July 2, 1912 2,152,989 Ewest et al. Apr. 4, 19392,164,183 Vain Liempt et al. lune 27, 1939 2,491,868 Martt Dec. 20, 19492,596,697 Krefft May 13, 1952 2,785,327 Anderson Mar. 12, 1957

